EP1631836B1 - Verfahren und vorrichtung zur simulation eines dopplersignals zum selbst-test eines ruhenden höhenmessers - Google Patents

Verfahren und vorrichtung zur simulation eines dopplersignals zum selbst-test eines ruhenden höhenmessers Download PDF

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Publication number
EP1631836B1
EP1631836B1 EP04754830A EP04754830A EP1631836B1 EP 1631836 B1 EP1631836 B1 EP 1631836B1 EP 04754830 A EP04754830 A EP 04754830A EP 04754830 A EP04754830 A EP 04754830A EP 1631836 B1 EP1631836 B1 EP 1631836B1
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EP
European Patent Office
Prior art keywords
signal
frequency
period
decimation
base band
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Expired - Lifetime
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EP04754830A
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English (en)
French (fr)
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EP1631836A1 (de
Inventor
James R. Hager
Lavell Jordan
Benjamin J. Winstead
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Honeywell International Inc
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Honeywell International Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/50—Systems of measurement based on relative movement of target
    • G01S13/52—Discriminating between fixed and moving objects or between objects moving at different speeds
    • G01S13/522—Discriminating between fixed and moving objects or between objects moving at different speeds using transmissions of interrupted pulse modulated waves
    • G01S13/524—Discriminating between fixed and moving objects or between objects moving at different speeds using transmissions of interrupted pulse modulated waves based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi
    • G01S13/53—Discriminating between fixed and moving objects or between objects moving at different speeds using transmissions of interrupted pulse modulated waves based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi performing filtering on a single spectral line and associated with one or more range gates with a phase detector or a frequency mixer to extract the Doppler information, e.g. pulse Doppler radar
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/882—Radar or analogous systems specially adapted for specific applications for altimeters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G01S7/285—Receivers
    • G01S7/288—Coherent receivers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G01S7/285—Receivers
    • G01S7/292—Extracting wanted echo-signals

Definitions

  • This invention relates generally to sampling techniques to determine Doppler frequencies, and more specifically to a radar altimeter which incorporates sampling techniques that overcome zero Doppler returns.
  • Known pulse Doppler radar altimeters process the received radar returns at a base band frequency to minimize the amount of data processed and to minimize processing speeds required to accurately process the radar returns.
  • only a Doppler shifted frequency remains after the radar return signal is converted to a base band frequency.
  • a zero Doppler frequency shift results in a DC level signal being provided to the base band processing circuits. The result is that the base band processing circuits provide no data that can be utilized to determine an altitude.
  • a radar altimeter operate properly with the aircraft stationary on the ground to allow preflight testing and calibration.
  • Other attempts have been made to rectify the zero Doppler frequency shift problem.
  • One known solution to the zero Doppler frequency shift problem includes mixing an output of a RF mixer local oscillator with a signal source whose signal output is approximately equal to the frequency of a Doppler shift that is typically encountered during a flight.
  • this solution requires that additional RF circuitry be added to the radar altimeter, which adds significant expense to the radar altimeter.
  • US4714928A discloses a radar altimeter circuit that includes, in combination, the features of claim 1 to augment an IF signal with a locally produced signal in segments of the IF signal that suffer from a return signal fade.
  • the invention consist in a radar altimeter comprising:
  • Figure 1 illustrates a down conversion to a base band frequency from an intermediate frequency (IF).
  • IF intermediate frequency
  • Such a down conversion is part of a processing sequence for a radar return signal received by a radar altimeter, and is sometimes referred to as decimation to a base band frequency.
  • down conversion to base band frequency is normally accomplished in a processor by sampling a return signal 10 at a period of length that is an integer multiple of the period of return signal 10.
  • the base band frequency is referred to as a Doppler frequency, as the base band frequency is the result of a Doppler shift in the IF.
  • return signal 10 has a period of slightly less than 40 nanoseconds, or is at a frequency of 25 MHz plus the base band (Doppler) frequency.
  • a radar altimeter which utilizes an IF frequency of 25 MHz could, for example, be sampled at 5 MHz, or 25 kHz, or 10 kHz, etc. Therefore, a sampling interval for return signal 10 is stated mathematically as n ⁇ 40 nanoseconds, where n is an integer.
  • return signal 10 is sampled about every four cycles of return signal 10. The sampling rate, shown by sample points 12 is therefore at an integer multiple of about 4 ⁇ 40 nanoseconds, or every 160 nanoseconds, which is a rate of 6.25 MHz.
  • the 6.25 MHz sampling rate is utilized for ease of illustration.
  • Other sampling rates could be used, for example, a sampling rate of 25 kHz, which is a sample once every 1000 cycles of the IF frequency of 25 MHz.
  • a sampling rate of 25 kHz which is a sample once every 1000 cycles of the IF frequency of 25 MHz.
  • lower sampling frequencies results in less signal processing, but the sampling frequency should be at least two times the highest expected Doppler frequency, to prevent aliasing.
  • Return signal 10 includes a Doppler shift of, for example, about 1000 Hz such that the frequency of return signal 10 is about 25.001 MHz. Sometimes an intermediate frequency added to a Doppler frequency is referred to as a shifted IF.
  • the Doppler shift causes return signal 10 to be sampled at slightly different points of the individual cycles that make up return signal 10. Samples 12 at the slightly different points of return signal 10 are utilized to generate a signal at the frequency of the Doppler shift.
  • a base band signal 14 is at the Doppler frequency, which is then processed by a radar altimeter to determine, for example, a change in amplitude of an aircraft.
  • Figure 2 illustrates the sampling of Figure 1 above, with no Doppler shift in return signal 20.
  • signal 20 includes no Doppler shift of the IF frequency
  • the frequency of signal 20 is constant at the intermediate frequency of 25 MHz.
  • signal 10 shown in Figure 1
  • signal 20 is sampled at a 6.25 MHz rate, or once every 160 nanoseconds.
  • 160 nanoseconds is an integer multiple of the period (40 nanoseconds) of signal 20
  • sampling points 22 occur at about the same location within individual cycles of return signal 20.
  • a signal 24 that is generated from such samples is therefore a DC signal, which cannot be processed by known radar altimeter processors, as no base band frequency results.
  • signal 24 is sometimes referred to as a zero return signal.
  • a zero return signal is received at a processor of a radar altimeter, is when the radar altimeter is stationary, for example, an aircraft parked on a runway.
  • zero return signals make it difficult to perform preflight testing and calibration procedures.
  • FIG. 3 is a block diagram of a radar altimeter 50, which compensates for the zero return signal problem described above.
  • radar altimeter 50 is incorporated in an air vehicle.
  • Radar altimeter 50 includes filter/driver 52, clock 54, temperature sensor 56, transmit antenna 58, transmitter 60, driver 61, sequencer 62, processor 64, receive antenna 66, receiver 68, driver/sensitivity range control (SRC) filter 69, intermediate frequency (IF) amplifier-filter 70, digitizer 72, memory 74 and transmit power filter/driver 76.
  • SRC driver/sensitivity range control
  • Transmitter 60 transmits pulses of RF energy towards the ground through antenna 58.
  • the RF energy is modulated with a pulse compression Bi-phase coded format produced by sequencer 62 resulting in modulated radar signals.
  • the output power of transmitter 20 is controlled in a closed loop fashion by processor 64, which is coupled to transmit power filter/driver 76.
  • the output power of transmitter 60 is minimized by processor 64 for a low probability of detection.
  • Antenna 66 receives the modulated radar signals reflected from the ground.
  • the received signals are amplified and mixed down to IF by receiver 68, and further amplified and band limited by IF amplifier-filter 70.
  • Digitizer 72 digitizes the received signal, as described above with respect to Figures 1 and 2 , and outputs the digitized samples to memory 74.
  • Sequencer 62 selects ground return samples corresponding to a present altitude delay (as determined by processor 64 and communicated to sequencer 62 on an internal range line) and shifts the selected samples from memory 74 to processor 64. Processor 64 then determines if the next set of samples should be taken closer in or further out in range, and generates a new internal range command. The result is a closed-loop altitude tracking servo, such that as the altitude changes, processor 64 generates a measure of range tracking error which is used to change the internal range command fed back to sequencer 62. Processor 64 generates an output altitude from the internal range. In one embodiment, processor 64 includes decimation frequency logic, which is utilized in down sampling the IF frequency, which may include a Doppler shift, to a base band frequency.
  • FIG. 4 is a partial block diagram of processor 64.
  • processor 64 receives selected samples of the digitized IF frequency from memory 74, and further receives a clock signal.
  • Processor 64 includes a narrow band filter 80, a decimation to base band function 82, a radar altimeter processing function 84, and decimation frequency logic 86.
  • narrow band filter 80 removes noise from the samples, which are passed to decimation to base band function 82.
  • Decimation to base band function 82 receives a decimation period from decimation frequency logic 86, providing a base band signal which compensates for possible zero Doppler returns, to allow altitude processing by radar altimeter processing function 84.
  • decimation frequency logic 86 causes decimation to base band function 82 to sample the IF digital samples received from narrow band filter 80 at a frequency whose period is at an integer multiple of the period of the intermediate frequency plus a selected fraction of the period of the intermediate frequency.
  • decimation frequency logic 86 Operation of decimation frequency logic 86 is further illustrated by an example. If the highest expected Doppler frequency is about 12 kHz, a 25 kHz sampling frequency for decimation to base band could be utilized, which would prevent aliasing. For an IF frequency of 25 MHz, with a period of 40 nanoseconds, there are four 10 nanosecond samples per cycle. For a sampling frequency of 25kHz, with a period of 40,000 nanoseconds, there are 4,000 10 nanosecond samples per cycle. However, decimation frequency logic 86 causes the sampling rate to be changed, in one illustrative example, by adding an extra 10 nanosecond delay in between samples of the IF frequency.
  • Decimation frequency logic 86 in one embodiment, is programmable such that other fractions of the period of the IF signal can be utilized, for example, adding a 30 nanosecond delay in between samples of the IF frequency, for a sampling rate of about 24,981 Hz.
  • radar altimeter 50 By adjusting the sampling rate through decimation frequency logic 86, radar altimeter 50 (shown in Figure 3 ) is able to compensate for zero Doppler returns, as the adjusted sampling rate results in a non-zero base band frequency being provided to radar altimeter processing function 84, which then determines an altitude of the vehicle in which radar altimeter 50 is installed through utilization of known altitude processing techniques.
  • radar altimeter processor 84 For the processing of samples of IF frequencies which include a Doppler shift, in addition to the changed decimation period, radar altimeter processor 84 is configured to subtract the frequency resulting from the changed decimation period such that the actual Doppler frequency is utilized in determining an altitude of a vehicle incorporating radar altimeter 50.
  • FIG 5 illustrates a down conversion to a base band frequency from an intermediate frequency (IF) signal 150 in, for example, radar altimeter 50 (shown in Figure 3 ) for a zero Doppler condition.
  • radar altimeter 50 incorporates processor 64 (shown in Figure 4 ).
  • processor 64 shown in Figure 4
  • decimation frequency logic 86 shown in Figure 4
  • a base band signal 152 is generated under zero Doppler conditions by sampling IF signal 150 at a frequency whose period is an integer multiple of the period of IF signal 150 plus a carefully chosen fraction of the period of IF signal 150.
  • a base band frequency (e.g. signal 152) which results is offset from a frequency of an actual Doppler offset.
  • decimation frequency logic 86 Operation of decimation frequency logic 86 is further illustrated in the following example.
  • the fractional period of IF signal 150 chosen plus the integer multiple of IF signal 150 results in a 2.9 kHz base band signal 152. Therefore, under zero Doppler conditions, the samples 154 which constitute base band signal 152, cause signal 152 to be at a frequency of 2.9 kHz.
  • the samples 154 that constitute base band signal 152 result in a 3.9 kHz signal.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar Systems Or Details Thereof (AREA)

Claims (5)

  1. Radarhöhenmeßgerät (50), umfassend:
    einen Speicher (74);
    einen Sequenzer (62) zum Modulieren eines ersten Signals;
    einen an den Sequenzer gekoppelten Sender (60) zum Übertragen eines das modulierte erste Signal enthaltenden Radarsignals zum Boden;
    einen Empfänger (68) zum Empfangen eines reflektierten Radarsignals vom Boden, wobei das empfangene Radarsignal das modulierte erste Signal enthält;
    einen an den Empfänger gekoppelten Digitalisierer (72) zum Erzeugen von digitalen Proben (154) des modulierten ersten Signals bei einer Zwischenfrequenz (ZF) (150), wobei die digitalen ZF-Proben in dem Speicher gespeichert werden; und
    einen an den Speicher gekoppelten Prozessor (64), wobei der Prozessor die gespeicherten digitalen ZF-Proben bei einem ganzzahligen Vielfachen der Periode der gespeicherten digitalen ZF-Proben plus einem Bruchteil einer Periode der gespeicherten digitalen ZF-Proben abtastet.
  2. Radarhöhenmeßgerät (50) nach Anspruch 1, wobei der Prozessor (64) folgendes umfaßt:
    ein Schmalbandfilter (80), das die in dem Speicher gespeicherten digitalen ZF-Proben (154) empfängt;
    eine Dezimierung-zu-Basisband-Funktion (82), die die gefilterten digitalen ZF-Proben von dem Schmalbandfilter empfängt;
    eine Dezimierungsfrequenzlogik (86), die verursacht, daß die Dezimierung-zu-Basisband-Funktion die von dem Schmalbandfilter empfangenen digitalen ZF-Proben mit einer Frequenz abtastet, deren Periode ein ganzzahliges Vielfaches der Periode des ZF-Signals (150) plus einem ausgewählten Bruchteil der Periode des ZF-Signals ist; und
    einen Radarhöhenmeßgerätprozessor (84) zum Bestimmen einer Höhe auf der Basis eines von der Dezimierung-zu-Basisband-Funktion empfangenen Basisbandsignals (152), wobei das Basisbandsignal die durch die Dezimierung-zu-Basisband-Funktion genommenen Proben (154) darstellt.
  3. Radarhöhenmeßgerät (50) nach Anspruch 2, wobei der ausgewählte Bruchteil der Periode des ZF-Signals (150) in die Dezimierungsfrequenzlogik (86) programmiert werden kann.
  4. Radarhöhenmeßgerät (50) nach Anspruch 2, wobei das ganzzahlige Vielfache der Periode des ZF-Signals (150) in die Dezimierungsfrequenzlogik (86) programmiert werden kann.
  5. Radarhöhenmeßgerät (50) nach Anspruch 6, wobei der Bruchteil der Periode der gespeicherten digitalen ZF-Proben (154) ein negativer Bruchteil der Periode der gespeicherten digitalen ZF-Proben ist.
EP04754830A 2003-06-11 2004-06-09 Verfahren und vorrichtung zur simulation eines dopplersignals zum selbst-test eines ruhenden höhenmessers Expired - Lifetime EP1631836B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US10/459,138 US6753806B1 (en) 2003-06-11 2003-06-11 Methods and apparatus to compensate for zero Doppler returns
PCT/US2004/018336 WO2005001506A1 (en) 2003-06-11 2004-06-09 Methods and apparatus for simulating a doppler signal for self-testing an altimeter in stationary condition

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EP1631836A1 EP1631836A1 (de) 2006-03-08
EP1631836B1 true EP1631836B1 (de) 2009-04-08

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US (1) US6753806B1 (de)
EP (1) EP1631836B1 (de)
JP (1) JP2007500857A (de)
CA (1) CA2527272A1 (de)
DE (1) DE602004020464D1 (de)
WO (1) WO2005001506A1 (de)

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US6897803B2 (en) * 2003-06-11 2005-05-24 Honeywell International Inc. Radar altimeter with forward ranging capabilities
US7075478B2 (en) * 2004-06-07 2006-07-11 Honeywell International Inc. Radar altimeter having an automatically calibrated sensitivity range control function
US7138940B2 (en) * 2004-07-22 2006-11-21 Honeywell International Inc. Method and systems for automatic zero calibration of radar altimeters
RU2280263C1 (ru) * 2005-01-31 2006-07-20 Дмитрий Геннадьевич Митрофанов Способ селекции ложных воздушных целей
US7518547B2 (en) * 2007-07-16 2009-04-14 Honeywell International Inc. Method and system of interference detection for radar altimeters
US7777668B2 (en) * 2008-04-08 2010-08-17 Honeywell International Inc. Radar altimeter with forward looking radar and data transfer capabilities
RU2410715C2 (ru) * 2009-04-03 2011-01-27 Владимир Иванович Винокуров Способ распознавания сигналов, принадлежащих одной цели, и устройство для его осуществления
GB2478003B (en) 2010-02-23 2012-07-25 Torotrak Dev Ltd Variator traction control arrangement
RU2513868C2 (ru) * 2012-06-14 2014-04-20 4 Центральный научно-исследовательский институт Министерства обороны Российской Федерации (4 ЦНИИ Минобороны России) Способ обзорной импульсно-доплеровской радиолокации целей на фоне пассивных помех
EP3196676B1 (de) * 2016-01-22 2020-12-09 Bristol Industrial and Research Associates Limited Vorrichtung zur detektion von niederschlagsbedingungen
US10107896B2 (en) * 2016-01-27 2018-10-23 Rohde & Schwarz Gmbh & Co. Kg Measuring device and measuring method for measuring the ambiguity function of radar signals

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Also Published As

Publication number Publication date
JP2007500857A (ja) 2007-01-18
WO2005001506A1 (en) 2005-01-06
CA2527272A1 (en) 2005-01-06
DE602004020464D1 (de) 2009-05-20
EP1631836A1 (de) 2006-03-08
US6753806B1 (en) 2004-06-22

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